Research has been carried out into two aspects of the cerebral circulation: (1) Its neurogenic control and (2) the basis of cerebral vasospasm. Since small cerebral blood vessels may be quantitatively more important in the regulation of blood flow than larger vessels, our studies on the basilar artery have been extended to vessels as small as 100 microns O.D. An analysis of the adrenergic neuroeffector mechanis in these small vessels suggest that their main characteristics are similar to those of larger cerebral vessels. Cerebral vessels have both a constrictor and a dilator innervation: both have features not found in blood vessels from other regions. The basis of these unique features is being defined. An analysis is being carried out of the pathophysiology of cerebral vasospasm using two models. The first is the stretched rabbit basilar artery where in association with small discrete tears of the internal elastic lamina there is local prolonged constriction and the second, the vasospasm associated with subarachnoid hemorrhage in the monkey. This study involves both functional analysis of nerve and muscle together with a morphological survey. BIBLIOGRAPHIC REFERENCES: Bevan, J.A.: Some Functional Consequences of Variation in Adrenergic Synaptic Cleft Width and in Nerve Density and Distribution. Fed. Proc., 1977, in press. Bevan, J.A. and Bevan, R.D.: Response of Blood Vessels to Sympathetic Nerve Stimulation. Proceedings of Symposium on Molecular and Cellular Aspects of Vascular Smooth Muscle in Health and Disease. Karger, 1977, in press.